But a new study, published last month in the Journal of the American Medical Association, suggests a potential solution: Researchers found that people who took probiotics — a supplement with beneficial bacteria — along with their prescribed antibiotics were 42 percent less likely to develop diarrhea.

Here's what happens: Antibiotics indiscriminately wipe out both illness-causing bad bacteria and the good bacteria that naturally live in the gut and help keep the digestive tract in good working order. Over-the-counter probiotic supplements — acidophilus pills, for example — can replace the good bacteria.

Researchers analyzed the results of 63 studies involving nearly 12,000 people who needed antibiotic treatment, comparing those who took probiotic pills with those taking either a dummy pill or nothing. Although the researchers couldn't tell whether one type of probiotic bacteria was better than another, probiotics were clearly effective at preventing diarrhea.

The researchers did not compare the effectiveness of different types of supplements, says review coauthor Sydne Newberry, a nutritional scientist and researcher at RAND, in Santa Monica, Calif. Nor did they compare taking supplements versus eating yogurt with active live cultures, which also may replace some good bacteria. Yogurt wasn't used in any of the studies.

But even with these uncertainties, the review is helpful, says nutrition specialist Caroline Apovian, M.D., director of the Nutrition and Weight Management Center at Boston Medical Center, who was not involved in the research. An analysis that includes such a large number of people "provides statistically significant results about the benefits of probiotics," she says.

Because the majority of studies looked at preventing diarrhea rather than treating it once it began, Newberry recommends that patients begin taking a probiotic before starting their antibiotic medication.

For those who prefer to get their probiotics by eating yogurt, keep in mind that some yogurt is heat-treated to reduce tartness or extend shelf life, which kills the beneficial bacteria, Apovian says. To get the full benefit of yogurt's good bacteria, look for a label with "live active cultures."